This invention relates to the catalytic partial oxidation of olefinic hydrocarbons directly to their corresponding unsaturated carbonyl compounds, e.g. aldehydes and ketones. More specifically, this invention relates to a process for improving the selectivity to unsaturated aldehydes and ketones by reacting olefinic hydrocarbons and a source of oxygen on a novel bimetallic catalyst system which is composed of a combination of gold and copper. Other partial oxidations for which this catalyst is useful include the oxidation of aromatics to their corresponding aldehydes, e.g., toluene to benzaldehyde and xylene to tolualdehyde. In a preferred embodiment of this invention, acrolein is selectively prepared by passing a mixture of propylene and a source of oxygen over a supported gold-copper bimetallic catalyst system.